King Willem-Alexander, 50, said he has ended his role as a regular First Officer after 21 years on KLM's fleet of Fokker 70 planes. He will now retrain to fly Boeing 737s as the Fokkers are being phased out of service. (dailym.ai) Más...

I think it's cool that the King got to do what he loves, but is flying twice a month sufficient to maintain proficiency? And, now that the news is out more widely, wouldn't his continued role as a co-pilot make his flights a target?

well well, King Willem being instructed how to pilot the Boeing 737 now that Fokker is being phased out. The flying Dutchman will always stay alive .The first twin engine Fokker was presented to queen Beatrix 40 years ago.Soesterberg is a small upscale town where the King has his palace and is staffed by American Pilots using the F-15 Jet fighters. Do not worry, the King is well protected.

Like others here I think it's great that he has this outlet & diversion.. However, with flying only twice a month ( maybe less at times due to official responsibilities? ) It seems difficult to gain & maintain proficiency in a commercial situation where he is assuming responsibility for the lives of his passengers.

He is the First Officer (co-pilot) and there is a fully qualified Captain in the left seat I would imagine. So, not a problem as he is not on his own! See also my post above for definition of proficiency and/or currency.